Method of controlling the residual magnesium content of nodular graphite cast iron



Patented Oct. 24, 1950 MAGNESIUM CONTENT OF NODULAR GRAPHITE CAST IRON James Fernando Jordan, Huntington Park, Calif.,

assignor to James Jordan Laboratory, Huntington Park, Calif a partnership .f

No Drawing. Application August 12, 1949,

Serial No. 110,026

.5Claims. (01.175430) j My invention relates to the commercial pro- -duction of nodular graphite cast iron.

The advantages to be gained from the convers1on of the graphite content of grey cast ironfrom the usual flake form to the nodular or rounded form have been widely publicized in recent years, and it has become abundantly clear that if a method of controlling the residual magnesium content of greycast iron :could be found, the large scale production of this new ferrous metal would be assured. With this. in mind, metallurgists have been carrying on an intensive search for a simple method of controlling the residual magnesium content of molten cast iron.

I have discovered such a control method. I

have found that when the magnesium is introduced into the molten ironin the form of a gaseous mixture consisting of magnesium gas and an inert gas, the residual magnesium content of the molten metal may be controlled by conaquiet and efficient operation. In the first test,

sampling of the metal bath showed that, while the magnesium content of the metal remained very low during the period when the magnesium was desulphurizing the metal, the magnesium content of the metal rapidly rose after the desulphurizing operation reached equilibrium, and

that the magnesium content of the metal continued to rise until it reached a level above which further introductions of the magnesium-bearing gas failed to increase the magnesium valuein other Words, after a certain magnesium value was reached, the magnesium-bearing gas seemed incapable of introducing more magnesium into the molten metal.

At first it was thought that when the magnesium content of the bath leveled oil, saturation had been reached. however, the magnesium content of the second test leveled oil at an entirely different value. Investigation showed that the main difference between the two tests was that the magnesiumhelium ratio in the gas stream passed into the In repeating the test,

two tests varied-that is, the magnesium'content of the helium stream employed in the first test was difierent from the magnesium content ofthe-stream employed in the second test.

These tests seemed to indicate that'I could control the residual magnesium content of the molten metal by controlling the magnesium content of the introduced mixture, In an attempt to confirm this, I ran a third test in which-I varied the magnesium content of the introduced mixture, allowingampletime between variations for the magnesium value in the metal to change. This third testshowedthat, while a given magnesium-helium-ratio Waslincapable of lifting the magnesium content of the metal above a value fixed by said ratio, by increasing the magnesium content of the gas mixture in steps, I was able to increase-the magnesium content-of the metal in steps, and thateach new magnesium-helium ratio was incapable of lifting the magnesium content of the metal above a value fixed by said ratio. In sh0rt, I was able to control the residualmagnesium content of the molten metal by controlling the magnesium content of said mixture.

It then occurred to me that the powdered magnesium content of the introduced mixture was evaporating to magnesium gas before said powder reached the molten metal, and that the mixture consisted of magnesium gas and helium gas by the timethat it. came intov actual contact with the molten iron. With this came the realization that something akin to the partial pressure law was in operation in thebath, and that all that was necessary, in order to make my control method effective, was to add the magnesiumto the inert gas stream in a manner that would assure that the magnesium was gaseous when the mixture contacted the molten metal.

In keeping with this, a fourth test was run wherein the magnesium was distilled into the metal bath from an alloy steel bomb, the gaseous magnesium being diluted with a fixed amount of helium as said gaseous magnesium passed from the bomb to the molten metal. As with the cases previously mentioned, the magnesium content of the metal bath leveled on when the magnesiumhelium ratio was substantially constant, and the magnesium content of the bath rose to a new fixed level when the distillation rate was increased by increasing the distillation temperature. The chilling effect arising from the introduction of cold helium into the stream of gaseous magnesium probably condensed at least a part of said gaseous magnesium, resulting in a situation at least partly similar to the process wherein powdered magnesium was directly employed.

The function of the helium in these tests is as an inert diluent for gaseous magnesium. By inert, I mean substantially non-oxidizing towards said gaseous magnesium. While I prefer helium because of its high thermal conductivity,

other inert gases may be employed, for example, argon or hydrogen. I ran one test using magnesium powder and carbon monoxide, and, while there apparently was a large wastage of the magnesium, due to a reaction between the magnesium and the carbon monoxide, the magnesium content of the metalwas fixed in accordance with the Mg-CO ratio. The expression "substantially inert is employed in my'claims.

to denote that degree of chemical inertness which permits my process to control the mag nesium content of the molten metal by means of the partial pressure of gaseous magnesium in the Mg-inert gas mixture.

The magnesium powder employed in these tests was the reagent grade, extracted with ether and alcohol to remove organic matter.

Other methods of introducing magnesium into a stream of inert gas will occur to those skilled in the art; for example, molten magnesium under pressure may be projected through an orifice into a stream of said inert gas, and said projection may be so arranged that the magnesium stream will be dispersed as a powder throughout the inert gas stream, so as to facilitate the evaporation of said magnesium before it contacts the molten iron.

Having now described my invention, I wish it to be understood that my invention is not to be limited to the specific steps or mixtures herein disclosed, except insofar as such limitations are specified in the appended claims.

I claim as my invention:

1. The method of controlling the magnesium content of molten iron, which comprises: mixing a substantially fixed amount of magnesium powder with a substantially fixed amount of gas that is substantially inert towards magnesium gas; leading the magnesium powder-inert gas mixture into said molten iron so that said magnesium powder is evaporated to magnesium gas before said mixture contacts said molten iron; and continuing to lead the magnesium gas-inert gas mixture into contact with said molten iron until said molten iron is substantially desulphurized by and substantially in equilibrium with said magnesium gas-inert gas mixture.

2. The method of controlling the magnesium content of molten iron, which comprises: mixing a substantially fixed amount of molten magnesium with a substantially fixed amount of gas that is substantially inert towards magnesium gas by atomizing molten magnesium into a stream of said inert gas; leading the magnesium-inert gas mixture into said molten iron so that said magnesium is evaporated to magnesium gas before said mixture contacts said molten iron; and continuing to lead the magnesium gas-inert gas mixture into contact with said molten iron until said molten iron is substantially desulphurized by and substantially in equilibrium with said magnesium gas-inert gas mixture.

3. The method of controlling the magnesium content of molten iron, which comprises: mixing magnesium gas with gas that is substantially inert towards magnesium gas to form a magnesium gas-inert gas mixture; and controlling the magnesium content of said molten iron by selectively increasing or decreasing the magnesium content of said gas mixture and then reacting said gas mixture with said molten iron until said molten iron is substantially desulphurized by and substantially in equilibrium with said gas mixture.

4. The method according to claim 3 in which said gas mixture is formed by mixing magnesium powder with said inert gas, said magnesium powder being evaporated to magnesium gas before the magnesium powder-inert gas mixture contacts said molten iron.

5. The method according to claim 3 in which said gas mixture is formed by mixing molten magnesium with said inert gas, said molten magnesium being evaporated to magnesium gas before the molten magnesium-inert gas mixture contacts said molten iron.

JAMES FERNANDO JORDAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,587,600 Nielsen June 8, 1926 1,931,144 Gilbert Oct. 17, 1933 2,003,487 Hansgirg June 4, 1935 2,224,160 Peake et a1 Dec. 10, 1940 2,238,907 McCom'ca et al Apr. 22, 1941 2,485,760 Millis et a1 Oct. 25, 1949 

1. THE METHOD OF CONTROLLING THE MAGNESIUM CONTENT OF MOLTEN IRON, WHICH COMPRISES: MIXING A SUBSTANTIALLY FIXED AMOUNT OF MAGNESIUM POWDER WITH A SUBSTANTIALLY FIXED AMOUNT OF GAS THAT IS SUBSTANTIALLY INERT TOWARDS MAGNESIUM GAS; LEADING THE MAGNESIUM POWDER-INERT GAS MIXTURE INTO SAID MOLTEN IRON SO THAT SAID MAGNESIUM POWDER IS EVAPORATED TO MAGNESIUM GAS BEFORE SAID MIXTURE CONTACTS SAID MOLTEN IRON; AND CONTINUING TO LEAD THE MAGNESIUM GAS-INERT GAS MIXTURE INTO CONTACT WITH SAID MOLTEN IRON UNTIL SAID MOLTEN IRON IS SUBSTANTIALLY DESULPHURIZED BY AND SUBSTANTIALLY IN EQUILIBRIUM WITH SAID MAGNESIUM GAS-INERT GAS MIXTURE. 